Process for the preparation of amino-1,3-benzenediol

ABSTRACT

High purity amino-1,3-benzenediols are prepared by (a) contacting a 1,3-bis(alkylcarbonato)benzene with a nitrating agent under reaction conditions such that a 1,3-bis(alkylcarbonato)nitrobenzene is formed, (b) contacting the 1,3-bis(alkylcarbonato)nitrobenzene with a hydrolyzing agent under conditions such that a nitro-1,3-benzenediol is produced, and (c) contacting the nitro-1,3-benzenediol with a reducing agent under conditions such that an amino-1,3-benzenediol is produced. Of the amino-1,3-benzenediols, 4,6-diamino-1,3-benzenediol is particularly useful in the preparation of high molecular weight polybenzoxazoles.

This is a continuation of application Ser. No. 110,754, filed Oct. 19,1987. BACKGROUND OF THE INVENTION

This invention relates to a process for the preparation ofamino-1,3-benzenediols and to novel intermediates used in theirpreparation.

Diaminobenzenediols and monoaminobenzenediols are useful as monomers forthe preparation of polybenzoxazoles. Polybenzoxazoles can be prepared byreacting diaminodihydroxybenzenes with bisacids, bisacid halides,bisesters or bisnitriles. In order to obtain a high molecular weightpolybenzoxazole which can be effectively spun into workable fibers, itis necessary that the starting materials used to form thepolybenzoxazoles are of very high purity. Polybenzoxazoles prepared fromhighly pure diaminobenzenediols can be spun into fibers having hightensile strength and thermal stability. Such fibers are desirable formilitary, aerospace and other applications requiring high performancematerials.

The traditional method for preparing 1,3-diamino-4,6-dihydroxybenzeneinvolves the treatment of 1,3-diacetoxybenzene with white nitric acid.The treatment with nitric acid results in the formation of theundesirable 2,4,6-trinitro-1,3-benzenediol and2,4-dinitro-1,3-benzenediol. Repeated recrystallizations are required toisolate the desired 4,6-dinitro-1,3-benzenediol from the undesirableby-products. The 4,6-dinitro-1,3-benzenediol is catalyticallyhydrogenated in dilute hydrochloric acid to produce the4,6-diamino-1,3-benzenediol. See Wolfe et al., Macromolecules, 14, p.909 (1981). This process is disadvantageous in that it requiresextensive purification and utilizes expensive starting materials.

Monoamino benzenediols are known to be useful as materials for makingdyes and are made by procedures similar to making diaminobenzenediolsand which similarly suffer from the same deficiencies for makingdiaminobenzenediols.

What is needed is an economical high yield process which results in theformation of a substantially pure amino-1,3-benzenediol. Such a processwould provide for the efficient production of amino-1,3-benzenediolswhich could be used to form the desirable high molecular weightpolybenzoxazoles.

SUMMARY OF THE INVENTION

The present invention is such a process for the preparation ofamino-1,3-benzenediols, particularly 4,6-diamino-1,3-benzenediols,2-methyl-4,6-diamino-1,3-benzenediol and 4-amino-1,3-benzenediol, inhigh purity and yield. In one aspect, the process of the presentinvention comprises (a) contacting a 1,3-bis(alkylcarbonato)benzene witha nitrating agent under reaction conditions sufficient to form a1,3-bis(alkylcarbonato)nitrobenzene, (b) contacting the1,3-bis(alkylcarbonato)nitrobenzene with a hydrolyzing agent underconditions sufficient to form a nitro-1,3-benzenediol and (c) contactingthe nitro-1,3-benzenediol with a reducing agent under conditionssufficient to form an amino-1,3-benzenediol. For the purposes of thisinvention, an "amino-1,3-benzenediol" is an aromatic diol having abenzene ring with a hydroxyl moiety in the 1- and 3- positions and atleast one amino moiety substituted on the benzene ring.

It has been discovered that the practice of this aspect of the inventioncan yield 4,6-diamino-1,3-benzenediol of unusually high purity which canbe utilized to prepare high molecular weight polybenzoxazoles. Whendesired, the practice of this aspect of the invention also can yield4-amino-1,3-benzenediol in high purity which is useful as a monomerintermediate for the preparation of polybenzoxazole ethers.

In another aspect, this invention is a process for preparing anitro-1,3-benzenediol which process comprises (a) contacting a1,3-bis(alkylcarbonato)benzene with a nitrating agent under reactionconditions sufficient to form a 1,3-bis(alkylcarbonato)nitrobenzene and(b) contacting the 1,3-bis(alkylcarbonato)nitrobenzene with ahydrolyzing agent under conditions sufficient to form anitro-1,3-benzenediol. Such nitro-1,3-benzenediols are useful asintermediates for making amino-1,3-benzenediols.

In a further aspect this invention is a1,3-bis(alkylcarbonato)nitrobenzene such as formed as an intermediate inthe aformentioned process.

DETAILED DESCRIPTION OF THE INVENTION

The 1,3-bis(alkylcarbonato)benzene employed as a starting material inthe practice of this invention is advantageously one wherein alkyl hasfrom 1 to 8 carbons, preferably from 1 to 4 carbons, most preferablymethyl and represented by the structure ##STR1## wherein R is hydrogenor alkyl having from 1 to 3 carbons, preferably methyl. The1,3-bis(alkylcarbonato)benzene is advantageously prepared by contactingresorcinol with an alkyl haloformate under any conditions sufficient toform the desired 1,3-bis(alkylcarbonato)benzene. For example, suitableconditions for making the desired biscarbonates are described by Meyerset al. in Tetrahedron Lett., 1375 (1978). Preferably, the desiredbiscarbonates are formed by adding an alkyl haloformate, most preferablymethyl chloroformate, to a reactor containing resorcinol(1,3-dihydroxybenzene) and sodium hydroxide in a mixture of water andmethylene chloride. The reaction mixture is preferably maintained at atemperature at or below 15° C.

The nitration step of the process of the present invention involvescontacting a 1,3-bis(alkylcarbonato)benzene with a nitrating agent underconditions sufficient to form the corresponding1,3-bis(alkylcarbonato)-4,6-dinitrobenzene. Any nitrating agent whichwill nitrate the 1,3-bis(alkylcarbonato)benzene at the 4 and 6 positionsunder the reaction conditions described herein can be utilized in thefirst step of the present invention. Suitable nitrating agents includealkali metal nitrates such as sodium and potassium nitrate and nitricacid at various concentrations, such as fuming nitric acid andconcentrated nitric acid. Concentrated nitric acid, e.g., from about 60to about 75 weight percent nitric acid, especially about 70 weightpercent, is the most preferred nitrating agent.

Advantageously, the nitrating agent is employed in combination with anacid other than nitric acid. Any other acid which, in the presence ofnitric acid, will facilitate the formation of nitronium ions under thereaction conditions described herein can be utilized in the first stepof the present process. Preferred such other acids for this purposeinclude trifluoroacetic acid, hydrochloric acid and sulfuric acid, withhydrochloric acid being more preferred and sulfuric acid being mostpreferred.

Suitable molar ratios of the nitrating agent to the1,3-bis(alkylcarbonato)benzene (hereinafter also referred to as thebiscarbonate) are those sufficient to cause the substitution of 2 nitrogroups on the benzene ring at the proportion of 2 nitro groups permolecule of the biscarbonate. Preferably, such ratios are those in therange from about 2:1 to about 3.3:1, with about 2.1:1 to about 2.8:1being more preferred. The most preferred ratio is 2.5:1. The amount ofthe other acid used in the nitration step is advantageously any amountwhich will generate NO₂ ⊕ in sufficient concentration to fully dinitratethe biscarbonate. Preferred molar ratios of the other acid, preferablysulfuric acid, to the biscarbonate are in the range from about 9.5:1 toabout 20:1, with about 10.5:1 to about 15:1 being more preferred. Themost preferred ratio is 11:1.

The temperature of the nitration step can be any temperature at whichnitration will occur. Preferred temperatures are in the range from about-5° C. to about 90° C., with from about 0° C. to about 40° C. being morepreferred. The pressure of the nitration step can be any pressure atwhich nitration will occur. Preferred pressures are about atmospheric,although subatmospheric or superatmospheric pressures can be employed.

The 1,3-bis(alkylcarbonato)nitrobenzene, which may have one or two nitromoieties, produced in the nitration step can be isolated by conventionalprecipitation and filtration techniques and is typically obtained ingreater than about 80 percent purity, preferably greater than 85 percentpurity and most preferably greater than about 90.5 percent purity. Theproduct of the nitration step is typically obtained in yields greaterthan about 95 percent, preferably greater than about 97 percent and mostpreferably greater than about 99 percent based on the initialbis(carbonate). Upon removal of methylene chloride used in the nitrationstep, the 1,3-bis(alkylcarbonato)nitrobenzene can be immediatelyutilized in the hydrolysis step of the present invention without furtherpurification.

The 1,3-bis(alkylcarbonato)nitrobenzene produced in this step is a novelcompound and is represented by one of the formulae: ##STR2## wherein Ris hydrogen or alkyl or 1 to 3 carbons, preferably methyl.

The hydrolysis step of the present process involves contacting the1,3-bis(alkylcarbonato)nitrobenzene prepared in the nitration step witha hydrolyzing agent under conditions sufficient to hydrolyze thecarbonate moieties thereby forming hydroxyl moieties. Any hydrolyzingagent which will convert the carbonate moieties to hydroxyl moieties issuitable. Suitable hydrolyzing agents include alcohols such as loweralkanols, phenols, and mixtures of water and one or more alcohols orphenols. Examples of preferred lower alkanols include methanol, ethanol,propanol and butanol, with methanol and ethanol being more preferred andmethanol being the most preferred. The hydrolysis step is advantageouslycarried out in the presence of an acid which will catalyzetransesterification with the biscarbonate. Examples of acids which areadvantageously employed in the hydrolysis step include hydrochloricacid, sulfuric acid, tetraalkoxytitanates and solutions thereof insulfuric acid, with hydrochloric acid being the most preferred.

Suitable molar ratios of the hydrolyzing agent to the1,3-bis(alkylcarbonato)nitrobenzene are those sufficient to hydrolyzeboth carbonate moieties. Examples of preferred ratios are those in therange from about 1000:1 to about 1:1, with about 20:1 to about 5:1 beingmore preferred. The most preferred ratio is 10:1. Preferred molar ratiosof 1,3-bis((alkylcarbonato)nitrobenzene to acid are those sufficient toprovide catalytic activity at a satisfactory rate. Examples of preferredmolar ratios of 1,3-bis(alkylcarbonato)nitrobenzene to acid are those inthe range from about 1:1 to about 100:1, with about 1:1 to about 10:1being preferred. If base is employed instead of acid, a molar excess ofbase to starting material which is at least 4.5 or more is used. Whenacid is used as the catalyst, it is generally preferred to employ atetraalkoxytitanate in combination with the acid. No additional catalystis required when base is used as the catalyst.

The temperature of the hydrolysis step can be any temperature at whichhydrolysis will occur. Preferred temperatures are in the range fromabout 20° C. to about 100° C., with from about 30° C. to about 70° C.being more preferred. The pressure used in the hydrolysis step can beany pressure at which hydrolysis will occur. Preferred pressures aregenerally about atmospheric, although subatmospheric andsuperatmospheric pressures can be suitably employed.

The product, e.g., 4,6-dinitro-1,3-benzenediol, of the hydrolysis stepcan be isolated by conventional precipitation and filtration techniquesand is typically obtained in greater than about 95 weight percentpurity, preferably greater than 97 weight percent purity and mostpreferably greater than about 99 weight percent purity. The product ofthe hydrolysis step is typically obtained in yields greater than about85 mole percent, preferably greater than about 90 mole percent and mostpreferably greater than about 93 mole percent based on moles ofhydrolysis starting material, e.g., 1,3-bis(alkylcarbonato)nitrobenzene,charged into the reaction. The nitro-1,3-benzenediol can be utilized asis in the reduction step of the present invention. Alternatively, it maybe purified further by recrystallization from a suitable solvent such asmethanol, propanol or ethyl acetate, with propanol being preferred.

The reduction step of the present invention advantageously involvescontacting the nitro-1,3-benzenediol produced in the hydrolysis stepwith a reducing agent, preferably a hydrogenating agent, in the presenceof a reduction catalyst, preferably a hydrogenation catalyst. Thereduction step is preferably carried out in a solvent. The hydrogenatingagent can be any material which will supply hydrogen to the reaction.Suitable hydrogenating agents include hydride reducing agents such aslithium aluminum hydride, stannous chloride in concentrated hydrochloricacid, dissolving metal reducing agents such as zinc metal and amalgamsof sodium or cadmium, for example, and hydrogen gas. Of thehydrogenating agents, hydrogen gas is the most preferred.

The solvent which is preferably employed in the reduction step can beany solvent which will remain inert under reduction, preferablyhydrogenation, conditions. Suitable solvents include alcohols such asethanol, methanol and propanol, as well as alkylene glycols such asethylene glycol and carboxylic acids such as acetic acid, withcarboxylic acids being preferred. The most preferred solvent ispropanol.

The hydrogenation catalyst can be any material which contains a noblemetal and will catalyze the reduction of the nitro groups. Examples ofsuitable catalysts include noble metals on carbon, noble metal oxidesand noble metals supported on alkaline earth carbonates. Noble metalsherein refer to gold, silver, platinum, palladium, iridium, rhodium,mercury, ruthenium and osmium. Preferred catalysts includepalladium-on-carbon, platinum-on-carbon and platinum oxide. The mostpreferred hydrogenation catalyst is 10 weight percentpalladium-on-carbon. Preferred catalysts are those sold commercially ashydrogenation catalysts for the reduction or elimination of halogen froman aromatic.

The hydrogenation catalyst is employed in an amount which is sufficientto catalyze the conversion of starting material in the presence of ahydrogenating agent to the corresponding diaminobenzenediol. Typically,from about 0.001 to about 1 molar equivalents of catalyst are presentper equivalent of nitro-1,3-benzenediol. Preferably, from about 0.01 toabout 0.5 and most preferably from about 0.01 to about 0.1 equivalentsof catalyst are present throughout the reaction.

When reduction is achieved by hydrogen reduction, the amount ofhydrogenating agent employed in the reduction step is suitably an amountsufficient to convert all nitro moieties to amino moieties. Examples ofsuch suitable amounts include those in the range from at least about 600to about 2000 mole percent of reducing agent based on moles ofnitro-1,3-benzenediol, preferably from about 610 to about 650 molepercent.

Alternatively to hydrogen reduction, the nitro-1,3-benzenediol can bereduced by contacting the nitro-1,3-benzenediol with a reducing agentsuch as stannous chloride dihydrate in a strong acid such ashydrochloric acid under reduction conditions. Other acids such assulfuric acid can be substituted for hydrochloric acid. When using sucha reduction procedure, the reducing agent is preferably employed in therange from about to about 8:1 to about 6.5, most preferably from about7.5:1 to about 7:1 molar, equivalents of reducing agent per equivalentof nitrobenzenediol. The acid is preferably employed in an amount fromabout 100:1 to about 10:1, based on the amount of nitro moiety to bereduced.

Suitable concentrations of nitro-1,3-benzenediol in the reaction mediumare those sufficient to afford an efficient recovery of product.Examples of such suitable concentrations are those in the range fromabout 0.001 to about 10 M (molar), with from about 0.1 to about 2 Mbeing preferred. The most preferred concentration is 1 M.

The temperatures and pressures employed in the reduction step aresufficient to effect completion of the reduction. Preferably, thetemperature is in the range from about 0° C. to about 150° C., mostpreferably from about 30° C. to about 75° C. Pressures employed arepreferably from about atmospheric to about 300 psi, most preferably fromabout atmospheric to about 50 psi.

The amino-1,3-benzenediols can be recovered using known recovery methodssuch as precipitation and filtration. The product is generally isolatedand stored as a hydrohalide salt in order to prevent oxidativedecomposition. It is also suitable common practice to isolate theproduct as a salt of any mineral acid such as sulfuric, nitric orphosphoric acid. The amino-1,3-benzenediols produced in the practice ofthe present invention are typically obtained in a purity greater than 96weight percent, preferably greater than 98 weight percent, mostpreferably greater than 99 weight percent, with yields being typicallygreater than 90 mole percent, preferably greater than 95 mole percentand most preferably greater than 96 mole percent, based on moles of4,6-dinitro-1,3-benzenediol charged to the reaction.

SPECIFIC EMBODIMENTS

The following example is given to illustrate the invention and shouldnot be construed as limiting the scope. All parts and percentages are byweight unless otherwise indicated.

EXAMPLE 1 A. Carbonation of Resorcinol ##STR3##

To a 5-liter, 3-necked, round-bottom flask equipped with a mechanicalstirrer, condenser, thermometer and an addition funnel is charged whilestirring, one liter of methylene chloride (CH₂ Cl₂), one liter of asolution of 125 g of NaOH in water and 110 g (1 mole) of resorcinol. Theresulting mixture is cooled to 0° C. and 250 ml (3.24 moles) of methylchloroformate is added dropwise at a rate such that the temperature ofthe reaction mixture does not exceed 15° C. After 225 ml of the methylchloroformate is added, an additional 300 ml of a solution of 5.0 g ofNaOH in water and 10 ml of triethylamine is added to the reactionmixture while maintaining the temperature at 10° C. After this additionis completed, the remaining 25 ml of methyl chloroformate is added. Theorganic phase of the reaction mixture is washed with three (100-ml)portions of water and the methylene chloride phase which contains thereaction product is dried over MgSO₄ and then the methylene chloride isremoved in vacuo to yield 220 g of 1,3-bis(methylcarbonato)benzene whichis suitable for use without further purification.

B. Nitration of 1,3-Bis(methylcarbonato)benzene ##STR4##

To a 5-liter, 3-necked, round-bottom flask equipped with a mechanicalstirrer, condenser and addition funnel, is added 120 g (0.53 mole) of1,3-bis(methylcarbonato)benzene in one liter of methylene chloride andcooled to 0° C. using a constant temperature bath. A solution of 136 mlof concentrated nitric acid and 136 ml of concentrated sulfuric acid isadded dropwise to the flask with stirring at such a rate to maintain thetemperature at 5° C. or below. Upon completion of the addition, thereaction mixture is heated to 25° C. and allowed to stir overnight.Analysis by gas chromatography shows conversion tomononitro-1,3-benzenediol (95 percent:5 percent 4-nitro isomer:2-nitroisomer, respectively). If a monoamine-1,3-benzenediol is desired, thisproduct is then recovered and subjected to hydrolysis and reduction bythe procedures set forth in Part C and Part D of this example.

The 1,3-bis(methylcarbonato)dinitrobenzene is formed by charging anadditional 500 ml of concentrated sulfuric acid to the stirred reactionmixture containing the 1,3-bis(methylcarbonato)mononitrobenzene whilemaintaining the mixture at 25° C. The temperature is allowed to rise to40° C. and maintained at that temperature for 6 hours. The organic phaseis separated and washed 3 times with 250-ml portions of water, driedover MgSO₄ and evaporated in vacuo to yield 162 g of product consistingof 89 percent of 1,3-bis(methylcarbonato)-4,6-dinitrobenzene and 11percent of 1,3-bis(methylcarbonato)-2,4-dinitrobenzene. This material isused without further purification.

C. Hydrolysis of 1,3-Bis(methylcarbonato)nitrobenzene ##STR5##

A 5-liter, 4-necked round-bottom flask is charged with 160 g (0.5 mole)of the product of Part B of this example dissolved in one liter of amixture containing 400 ml of concentrated hydrochloric acid, 2 ml oftetrakis(n-butyl)titanate and a remaining amount of methanol. Thereaction mixture is stirred at reflux (˜67° C.) for 21/2 hours. Aftersuch period, 100 ml of distilled water is added and the stirred reactionmixture is cooled to 6° C. The solid product which is formed is removedby filtration and dried in air to yield 87 g of4,6-dinitro-1,3-benzenediol (98 percent yield based on the amount of1,3-bis(methylcarbonato)-4,6-dinitrobenzene isomer charged at a purityof 98.7 percent).

D. Hydrogen Reduction of Nitro-1,3-benzenediol ##STR6##

A one-liter Hastelloy C autoclave equipped with a gas dispersion stirrerand cooling coil is charged with 100.0 g (0.5 mole) of the4,6-dinitro-1,3-benzenediol, 500 ml of n-propanol, ˜7.0 g of 10 percentPd/C and 10.0 ml of H₂ O. The sealed reactor is charged with 50 psi ofH₂ and the temperature is brought to 40° C. and maintained between 40°C.-50° C. during the course of the reaction. After a brief inductionperiod, the uptake of hydrogen becomes extremely rapid and H₂ pressureis maintained at about atmospheric pressure during the reaction. Uponcompletion, no further uptake of H₂ is observed. The reactor is cooledto room temperature, opened and 300 ml of concentrated HCl containing˜10 g of SnCl₂.2H₂ O is added to the reaction mixture. The crude productwith the catalyst is isolated by filtration. This material is dissolvedin 200 g of H₂ O at 85° C. and the catalyst is removed by filtration. H₂O (100-300 ml) is added to the filtrate along with 500 ml of HCl and thecatalyst-free material is precipitated from the brown solution.Recrystallization may be carried out in the existing solvent or thesemi-pure material can be isolated and air dried to afford 100 g ofcrude diamino resorcinol dihydrochloride (predominantly4,6-diamino-1,3-benzenediol dihydrochloride in 95.0 mole percent yieldbased on the 4,6-dinitro-1,3benzenediol.

E. Recrystallization of Diamino Resorcinol Dihydrochloride (PBO Monomer)

A 100-g portion of crude product of Part D is added to 500 g of 3.5M HCland heated until dissolved. A 10-g portion of decolorizing carbon and 2g to 5 g of SnCl₂.2H₂ O are added and refluxing is continued for aperiod of 15 minutes. The carbon is removed by filtration and therecrystallizing solution is cooled to 0° C. The white needles areisolated by filtration under a N₂ blanket and dried to yield 85-95 g ofthe PBO monomer (due to the oxidative instability of this material it isrecommended that recrystallization be carried out just prior topolymerization) (85 to 90 percent yield based on the product of Part Dcharged.

F. Polymerization of PBO Monomer

Generally following the procedures outlined in U.S. Pat. No. 4,533,693,a 100-ml resin kettle is loaded with 4,6-diamino resorcinoldihydrochloride (5.00 g, 23.4 mmole) obtained from Part E of thisexample, terephthaloyl chloride (4.76 g, 23.4 mmole) and polyphosphoricacid of 77 weight percent P₂ O₅ (20.0 g). The polymerization isperformed under nitrogen with stirring using the following profile: 40°C., 2 hours; 20° C., 120 hours; 40° C., 22 hours; 50° C., 24 hours; +P₂O₅ (10.3 g), 95° C., 24 hours; 150° C., 24 hours; 190° C., 24 hours. Theresulting polymer solution exhibited stir-opalescence and readily formedfiber. Inherent viscosity=19.8 dl/g, in 25° C. methane sulfonic acid,c=0.05 g/dl.

EXAMPLE 2 A. Carbonation of Resorcinol

Into a 5-liter, 4-necked flask are charged 275 g of resorcinol, 1.5liters of methylene chloride and a mixture of 625 g of 50 percent NaOHand 750 g of deionized water. After cooling to 0° C., 500 ml of methylchloroformate is added dropwise at a rate sufficient to maintain thereaction temperature between 5° C. and 15° C. After addition iscomplete, a mixture of 250 g of 50 percent NaOH, 1250 g of deionizedwater and 20 ml of triethylamine is added. An additional 125 ml ofmethyl chloroformate is added and the mixture is heated to 25° C. andstirred for 20 minutes. The resulting creamy white mixture is allowed toseparate into two phases and the organic phase is removed for use in thefollowing nitration step.

B. Nitration

A 5-liter, 4-necked flask is charged with product obtained from part Aand cooled to 0° C. To the flask is slowly added 2860 g of concentratedsulfuric acid, and thereafter 250 g of concentrated nitric acid is addeddropwise at a rate sufficient to maintain the reaction temperaturebetween 10° C. and 20° C. When the addition is complete, the reactionmixture is heated to 25° C. and mixed for 2 hours. The mixture is thencooled to 0° C. and 1000 ml of deionized water is added dropwise at arate sufficient to keep the reaction temperature at 10° C.-20° C. Thereaction mixture is then allowed to separate into phases. The organicphase is withdrawn and subjected to vacuum to remove the solvent therebyyielding 821 g of a light yellow powder. The powder is determined bynuclear magnetic resonance to be predominantly (95 percent)4-nitro-1,3-bis(methylcarbonato)benzene.

C. Decarbonation

The 5-liter, 4-necked flask is charged with 410 g of the nitrationproduct of part B dissolved in 500 ml of methanol and cooled to 15° C.while adding 1200 ml of deionized water. When the reaction mixture iscooled to 15° C., a mixture of 700 g of 50 percent NaOH and 300 g ofdeionized water is added. After stirring the reaction mixture for onehour at 25° C., the temperature is increased to 44° C. and 25 g of 50percent NaOH is added. The mixture is then heated to 56° C. for 3 hours,cooled to 0° C. and 100 ml of concentrated HCl is added dropwise. Theresulting yellow precipitate is removed by filtration and washedrepeatedly with deionized water to yield 180 g of wet powder(4-nitro-1,3-benzenediol). The remaining half of the 821 g of theproduct of part B is similarly treated and recovered to provide 145 g ofyellow powder.

D. Reduction

Into a 5-liter, 3-necked flask is charged 180 g of the wet powderproduct of part C dissolved in 3 liters of n-propanol. After addition ofa palladium-on-carbon catalyst (5 g of 58 percent dispersion of catalystin water), hydrogen gas is bubbled into the reaction mixture producingan exotherm and a color change from green to red to black. As thereaction mixture turns black, the hydrogen uptake and exotherm ceasesand the reaction mixture is cooled to 25° C. A 10-g portion of stannouschloride dihydrate dissolved in 750 g of concentrated HCl is added. Thecatalyst is removed by filtration and the solvent is removed in vacuo toyield a gray cake (125 g dry). The 145-g portion recovered in the secondprocedure of part C is similarly treated and produces 112 g of graycake. The gray cake is recrystallized by dissolving 125 g of the cake in190 g of concentrated HCl containing 5 g of stannous chloride dihydrateand 2 g of activated carbon and heating the mixture to 100° C. for 15minutes. The mixture is filtered and the resulting supernatant is cooledto 0° C. and filtered to remove a white precipitate (110.2 g afterdrying in a vacuum oven). Nuclear magnetic resonance analysis of thewhite precipitate indicates it to be 4 -amino-1,3-benzenediol. Yield ofthe final product based on the amount of resorcinol (1,3-benzenediol) is65 percent overall.

EXAMPLE 3 Preparation Of 2-Methyl-4,6-Diamino-1,3-Benzenediol

Following the procedure of Example 2, 2-methyl-1,3-benzenediol isconverted to 2-methyl-4,6-diamino-1,3-benzenediol in a yield of 75percent.

EXAMPLE 4 Methyl cis PBO Homopolymer

In an inert environment, 2-methyl-4,6-diamino-1,3-benzenedioldihydrochloride (6.80 g, 29.9 mmoles), terephthaloyl chloride (6.08 g,29.9 mmoles), and polyphosphoric acid (28.6 g having 76.7 percent P₂ O₅)are loaded into a 100-ml resin kettle. Reaction is performed undernitrogen with mixture mechanically stirred and warmed with an oil bathto the following reaction profile: 40° C., 16 hours; 50° C., 24 hours;95° C., +P₂ O₅ (15.9 g), 24 hours; 135° C., 24 hours; 190° C., 24 hours.At the end of the reaction, the mixture exhibits increased viscosity andcan be formed into fibers. Inherent viscosity of the resultant polymeris 17.6 dL/g in methanesulfonic acid at a concentration of 0.05 g/dL anda temperature of 25° C. Upon heating the polymer in air at a heatingrate of 20° C./min, degradation occurs at 621° C.

EXAMPLE 5 Methyl cis PBO Copolymer

In an inert environment, 2-methyl-4,6-diamino-1,3-benzenedioldihydrochloride (1.71 g, 7.51 mmoles), 4,6-diamino-1,3-benzenedioldihydrochloride (8.00 g, 37.6 mmoles), terephthaloyl chloride (9.15 g,45.1 mmoles), and polyphosphoric acid (40.2 g) having a phosphorouspentoxide content of 76.4 percent are loaded into a 10-ml resin kettle.Reaction is performed under nitrogen while stirring and heating thereaction according to the following profile: 40° C., 16 hours; 50° C.,24 hours; 95° C., +P₂ O₅ (23.5 g), 24 hours; 150° C., 24 hours; 190° C.,24 hours. At the end of the reaction, the reaction mixture exhibitsincreased viscosity and can be formed into fibers. Inherent viscosity ofthe copolymer is 15.9 dL/g in methanesulfonic acid at a concentration of0.05 g/dL and 25 C.

What is claimed is:
 1. A process for the preparation ofamino-1,3-benzenediol in high purity comprising the steps of(a)contacting a 1,3-bis(alkylcarbonato)benzene with a nitrating agent underreaction conditions sufficient to form a1,3-bis(alkylcarbonato)-nitrobenzene in a yield of at least 95 weightpercent based on the weight of the 1,3-bis(alkylcarbonato)benezene; (b)contacting the 1,3-bis(alkylcarbonato)nitrobenzene with a hydrolyzingagent under conditions sufficient to form a nitro-1,3-benzenediol; and(c) contacting the nitro-1,3-benzenediol with a reducing agent underconditions sufficient to form an amino-1,3-benzenediol.
 2. The processof claim 1 wherein the 1,3-bis(alkylcarbonato)benzene is1,3-bis(methylcarbonato)benezene.
 3. The process of claim 1 wherein thenitrating agent is nitric acid, and sulfuric acid is also employed inthe nitration step.
 4. The process of claim 1 wherein the hydrolyzingagent is a lower alkanol.
 5. The process of claim 4 wherein the loweralkanol is methanol.
 6. The process of claim 1 wherein4,6-diamino-1,3-benzenediol is recovered in a purity of at least 99weight percent.
 7. The process of claim 1 wherein4,6-diamino-1,3-benzenediol is recovered in a purity of at least 99.9weight percent.
 8. The process of claim 3 wherein the molar ratio ofconcentrated nitric acid to the 1,3-bis(alkylcarbonato)benzene is in therange of about 2:1 to about 3.3:1, the molar ratio of sulfuric acid tothe 1,3-bis(alkylcarbonato)benzene is in the range from about 9.5:1 toabout 20:1 and the temperature in step (a) is in the range from about-5° C. to about 40° C.
 9. The process of claim 5 wherein the molar ratioof methanol to the 1,3-bis(alkylcarbonato)nitrobenzene is in the rangefrom about 5:1 to about 100:1 and the temperature in step (b) is in therange from about 20° C. to about 100° C.
 10. The process of claim 1wherein the mole ratio of hydrogen gas to the nitro-1,3-benzenediol isin the range from about 6:1 to about 20:1, the molar equivalent ratio ofthe hydrogenation catalyst to nitro-1,3-benzenediol is in the range fromabout 0.001:1 to about 1:1 and the temperature used in step (c) is fromabout 0° C. to about 150° C.
 11. The process of claim 1 wherein thenitro-1,3-benzenediol is 4-nitro-1,3-benzenediol and theamino-1,3-benzenediol is 4-amino-1,3-benzenediol.
 12. The process ofclaim 1 wherein the nitro-1,3-benzenediol is2-methyl-4,6-dinitro-1,3-benzenediol and the amino-1,3-benzenediol is2-methyl-4,6-diamino-1,3-benzenediol.